Electron discharge device



June 23, 1959 Filed Oct. 4. 1955 3 Sheets-Sheet 1 INVENTORS Carl F. Miller 6 William H. McCurdy.

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3 Sheets-Sheet 3 Filed Oct. 4; 1955 m um United States Patent ELECTRON DISCHARGE DEVICE Carl F. Miller, Bath, and William H. McCurdy, Horseheads, N.Y., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvania Application October 4, 1955, Serial No. 538,442 Claims. (Cl. 313-378) This invention relates to electron discharge devices and more particularly to those devices having more than one complete electrode structure within a single envelope.

It is an object of this invention to provide an improved electrode assembly structure for a multiple-type electron discharge device.

It is another object to provide an improved internal shield structure between electrode structures of the multiple-type electron discharge device.

It is another object to provide improved shielding between separate electrode structures within the same envelope in order to increase the frequency of operation.

It is another object to provide an improved electrode assembly for multiple-type electron discharge devices that is less susceptible to shock and handling.

It is another object to provide an improved electrode structure adapted to ease of assembly.

It is another object to provide an improved electrode assembly of dual-type electron discharge devices suitable for automatic assembling operations. 7

It is another object to provide anelectrode assembly structure to decrease shrinkage in manufacture of electron tubes due to non-uniform spacing between the cathode and first grid.

These and other objects are effected by our invention as will be apparent from the following description taken in accordance with the accompanying drawings throughout which like reference characters indicate like parts, and in which:

Fig. 1 is a side view of an electron discharge device illustrative of one specific embodiment of our invention;

Fig. 2 is a sectional view of Fig. 1 taken along the line II-Il;

Fig. 3 is a detail view of a portion of the shielding structure and cathode shown in Fig. 1;

Fig. 4 is a plan view of an electron discharge device illustrative of another specific embodiment of our invention;

Fig. 5 is a side view of the device shown in Fig. 4;

Fig. 6 is a plan view partly broken away of an electron discharge device illustrative of another specific embodiment of our invention; and

Fig. 7 is a side view partly broken away of the device shown in Fig. 6.

Referring in detail to Figs. 1, 2 and 3 of the drawings, there is shown an electron discharge device constructed in accordance with the teachings of our invention. The electrode assembly 14 is enclosed within a suitable envelope 10, such as that used in the conventional miniature tube type structure. The envelope is of a suitable material, such as glass, and consists of a cylindrical body portion 16 closed at the lower end with a button stem 12 through which are sealed the various terminal prongs 18. These prongs 18 are connected on the interior of the envelope 10 to the various electrode elements of the mount structure and act as lead-in members as well as support members for the electrode assembly 14. Prefer ably, the prongs 18 have welded to their inner ends short metal extensions which can be easily bent to any desired position and thereby making connection to the various electrodes. The top of the envelope 10 is provided with an exhaust tubulation (not shown) and is sealed 013? after evacuation in conventional manner.

The electrode assembly 14 which is enclosed Within the envelope 10 illustrated in this specific embodiment is a multiple type assembly and more specifically a triodepentode. The electrode assembly 14 may be considered as comprised essentially of two compartments or portions, as illustrated in Figs. 1 and 2. The left-hand portion is the triode electrode structure and the right-hand portion is the pentode electrode structure. The triode structure and pentode structure utilize a common heater element 20 for their separate cathode structures 22 and 24 and a common support structure for their electrode elements.

The electrode elements of the pentode structure and the triode structure are positioned by means of a lower insulating spacer disc 26 and an upper insulating spacer disc 28. The spacer discs or wafers 26 and 28 which may be of any suitable material, such as mica or ceramic, are positioned substantially perpendicular to the longitudinal axis of the envelope 10 and parallel to each other. in a well known manner, the circular insulating spacers 26 and 28 are provided with apertures or openings to receive the ends or extensions thereon of the various electrode elements of the triode structure and the pentode structure, and thereby position the electrodes within the electrode assembly 14. Projections 30 may be provided around the periphery of the spacers 26 and 28 to form a spacer contact with envelope 10.

Between the two spacers 26 and 28 are situated the electrodes of the pentode structure and the triode structure. The active portions of the electrodes or elements are substantially parallel to-each other and perpendicular to the spacers 26 and 28. The electrode assembly 14 is constructed so that the active portions of elements of the pentode structure and thetriode structure are disposed between the spacers 26 and 28 and substantially separated by a centrally located planar shielding member 32 to form essentially two separate electrostatic shielded compartments.

The shielding member 32 is comprised of two planar insulating members 34 of a suitable material, such as ceramic or glass, and of aconfiguration as illustrated in Fig. 3. The planar insulating members 34 have a slot 38 of rectangular shape out or stamped out along one of the small dimension edges to form essentially a U-shaped member. This cutout slot 38 is provided for the positioning of cathodes 22 and 24 of the triode and pentode structures, respectively. The planar insulating member 34 illustrated in Fig. 3 has one surface coatedwith a metallic conductive layer 40. The metallic coating 40 is provided on only one of the planar insulating members 34 and is sandwiched between the two insulating members 34 when assembled. The metallic coating 40 is omitted on the portions 42 of metalized surface of the insulating member34 near the top and bottom of the slot cutout 3:8 to allow positioning of mounting tabs 44 provided on the cathodes 22 and 24 on an insulated surface.

The cathodes 22 and 24 provided for the triode an'd pentode structure are of similar configuration and each comprises essentially a half cathode structure which is electrically separated units with a common heater 20. The cathodes 22 and 24 consist of a metallic channeled, rectangular support member 46 of material, such as nickel, with an electron-emissive coating 48 deposited on the unchanneled surface. The dimensions ofthe cathodes 22 and 24 are slightly less than that of the slot cutout 38 to allow the cathodes 22 and 24 to be positioned within the slot 38. As shown in Fig. 3, tabs 44 are provided on the flange or channel wall portions at each corner of the metal support members 46 for positioning and retaining the cathodes 22 and 24 by means of the two insulating members 34. The cathode tabs 44 provided on the two cathodes 22 and 24 are staggered so that when the two cathodes 22 and 24 are positioned between the two insulating members 34, the tabs 44 of the respective cathodes 2t) and 24 will be separated sufliciently to give good electrical insulation. One of the cathode tabs 44 on each of the cathodes 22 and 24 also provides means of electrically connecting each cathode 22 or 24 to separate lead-in members 18. It is, therefore, shown clearly in Fig. 2 that the cathodes 22 and 24 are held securely by the two insulating members 34 under compression force when the two insulating members 34 are pressed together. The metal support member 46 may be of sufficient length or have tabs provided thereon to extend through apertures provided in both spacers 2-6 and 28.

The metallic coating 40 on the inner surface of one of the insulating members 34 is provided with a terminal and is connected to one of the various lead-in conductors 18 for purposes of grounding the metallic layer 40 and thus forming an effective electrostatic shield between the triode and pentode structure. The heater element 20 which is inserted within the channel portion of the two cathodes Z2 and 24 may also be grounded and thereby serve as an additional shield between the two cathodes 22 and 24 of the pentode and triode structures. This may be desirable in order to decrease the cathode to cathode capacitance to a minimum. Although the metallie shield 40 may be in the form of a metallic coating between the two insulating members 34, it may be desirable that a metal foil or a metal mesh be punched to the desired shape and inserted between the two insulat ing members 34. Such a self-supporting shield could be extended beyond the boundaries of the insulating members 34 to reduce the mass or cost of the structure and also enhance the shielding between the triode and pentode structures. The two insulating plates 34 may be fastened or bound to each other in any suitable manner such as clamping members or a cement.

A channel 50 is provided on the exterior surface of each of the two insulating members 34 in a manner shown in Fig. 2 and is also centrally located with the walls of the channel parallel to the long dimension of the cutout slot 38 in the insulating members 34. The channel 50 is of a greater width than the short dimension of the slot 38, and thereby provides a seat for the positioning of the control grids 52 and 54 of the pentode and triode structures, respectively. The channel provides means for accurately positioning the grids 52 and 54 with respect to the electron-emissive surface 48 on the cathodes 24 and 22. The depth of the channel 50 determines the spacing between the cathode 22 or 24 and the respective control grid 54 or 52 and thereby necessarily the transconductance of the electrode structures.

The control grids 52 and 54 in the pentode and triode are of planar type structure comprised of a rectangular frame of suitable material with an inner planar electron permeable active portion 56 in the form of parallel wires or mesh. The sides of the frame adjacent the channel walls are provided with an outturned flange to facilitate assembly and increase the mounting stability of the control grids 52 and 54 within the electrode structures. It may be desirable that the flange be made of a resilient construction so that the control grids 52 and 54 may be snapped into the channels 50 within the insulating members 34. The frame may be of sufficient length or extensions may be provided thereon to allow insertion into the opening within spacers 26 and 28. It is, therefore, seen that there is provided a new and improved multiple unit tube having a unitary grid, cathode and shield assembly having a high accuracy control of grid to cathode spacing and thereby more uniformity in the tube manufacturing assembly.

The triode assembly is completed with the provision of an anode 60 having a planar active area 62 parallel to and spaced from the control grid 54. The anode 60 has a cross section of a lJ-shaped member with oppositely extending portions 64 on the legs with the intermediate portion of the U-shaped member serving as the active portion 62. The oppositely extended portions 64 are of sufiicient length to extend through apertures provided in the spacers 26 and 28 or tabs may be utilized.

The pentode tube structure is completed with conventional type electrode structures consisting of a screen grid 70, a suppressor grid 72 and an anode 74 spaced from and in the order named from the control grid 52. The active areas 76, 78, of the respective screen grid '78, suppressor grid '72 and anode 74 being substantially planar and parallel to the active area 56 of the control grid 52. The electrode elements 70, 72 and 74 are also positioned by extending a portion of the electrodes or providing tabs to extend through the spacers 26 and 28.

Referring in detail to Figs. 4 and 5, there is shown a modified structure which incorporates improvements over that shown in Figs. 1, 2 and 3. The device consists of an envelope 10 of similar structure as that described with respect to Figs. 1, 2 and 3 in which the lower portion of the envelope 10 is closed with a button stem 12 through which are sealed the various tube prongs 18. These prongs 18 are connected interiorly of the envelope to the various electrodes and act as lead-in members, as well as support for the electrode assembly 71. The electrode assembly 71 illustrated in Figs. 4 and 5 is comprised of a twin triode structure in which the triode structures 73 and 75 are completely shielded from each other. The two triode structures 73 and 75 are identical, and the description will be limited to the front triode structure 75 positioned to the front of a shielding member '77 in Fig. 4. The shielding member 77 in this embodiment is comprised of a self-supporting metallic member of a suitable material, such as nickel plated steel or nickel, positioned substantially in the center of the envelope 10 and parallel to the longitudinal axis of the envelope. The shield 77 is of such dimensions as to extend sidewise and lengthwise well beyond the boundaries of any of the electrode elements within the electrode assembly 71.

For the purpose of spacing the electrode elements of the triode 75 comprised of a cathode 81, a control grid 82 and an anode 84, a pair of spacers 86 and 88 are positioned and retained on the front side of the shielding member 77 and separated by a small distance. The spacing members 86 and 88 are formed from a block of insulating material, such as mica or ceramic, having a cross section essentially in the form of a sector of a circle in which the angle between the radii is less than 90. By utilizing this type of configuration, the curved or arcuate edge of the spacers 86 and 88 is adjacent to the tube envelope wall 10, while one tapered side is positioned against the shielding member 77 and the other tapered side, which may be termed the opposing edges of the two spacer members 86 and 88 are positioned so that the electrode elements are retained between the opposing edges of the two spacer members 86 and 88. The spacers 86 and 88 may be held on the outside of the shielding member 77 by integral brackets stamped from the shield 71. In the specific embodiment shown, the spacers 86 and 88 are held on the outside to the shielding member by the integral brackets 90 stamped from the shield 77 and bent over a ridge provided on the curved edge while integral tabs 92 hold the spacers 86 and 88 to the shield 77 on inside ridges provided in the opposing edges of the spacing members 86 and 88.

The cathode 81 is positioned within notches 96 provided in the opposing edges of the two spacer members 86 and 88. In the specific embodiment shown, the cathode 81 is comprised of a tubular metallic sleeve 98 having a rectangular cross section with an electron-emissive coating 100 positioned on one of the larger dimensioned sides of the rectangular sleeve 98, and remote from the side adjacent the shielding member 77. A heater 94 is provided within the sleeve 98. Flanges are provided on the small dimension sides of the rectangular sleeve 98 for insertion into the notches 96 provided on the opposing edges of the spacer members 86 and 88. The cathode 81 is mounted so that the plane of electron-emissive surface 100 is substantially parallel to the shielding member 77. The uncoated larger dimensioned side is adjacent the shielding member 77.

Positioned adjacent to the cathode 81 and parallel to the electron-emissive coated surface 100 is the control grid 82. The contrcr grid 82 is of a planar type structure and consists of a frame 102 of sheet-like materal which supports and positions the planar active portion 104 of the grid. The active portion 104 consists of lateral wires or a mesh structure across the opening in the rectangular frame member 102. The active section 104 of the grid 82 is attached by conventional means, such as notching and peening, or brazing, to the frame member 102. Notches 106 are also provided on the opposing edges of the spacer members 86 and 88 for the insertion and positioning of the control grid 82.

Positioned adjacent to the control grid 82 on the remote side there with respect to the cathode 81 is the anode member 84 which has a planar active portion 110 substantially parallel to the control grid 82. The plate member 84 is also provided with positioning notches 116 within the opposing edges of the spacer members 86 and 88 as is shown in the specific embodiment. Extensions 114 from the active portion 110 of the plate 84 provides a means of securely seating the plate 84 within the notches 116 and provide a resilient mounting. V

In the assembly of the structure shown in Figs. 4 and 5, a subassembly consisting of the shielding member 77 and the spacer elements 86 and 88 is assembled and fastened together by means of the outside brackets 90 and the integral tabs 92. The shielding member 77 and the spacer members 86 and 88 are both rugged enough that, they may be transported in hoppers and assembled by mechanical means. The next operation in the assembly of the electrode structure would be the sliding of the tube elements into the proper slots or notches 96, 106 and 116 provided within the spacer members 86 and 88. A preferred sequence of mounting of the electrode members would be the cathode 81, then the grid 82, and then the plate member 84. It may be desirable that arbors or mechanical fingers pick up these tube components from loading positions and insert them into the spacers 86 and 88 with predetermined strokes to control the longitudinal alignment of all parts within one triode structure. The electrode assembly could then be rotated 180, and the same sequence repeated with the other triode structure.

The shielding member 77 extends well beyond the boundaries of the electrode elements and is connected to one of the various lead-in members 18. This lead-in member 18 may be grounded on the exterior of the envelope 10. It should also be noted that the structure allows the shield 77 to come in close proximity to the top of the button stem 12 and thereby makes a very effective electrostatic barrier against couplings of the inner portions of the lead-in conductors 18.

The structure described in Figs. 4 and 5 makes use of ceramic spacer members 86 and 88 which accordingly makes a much more rugged and serviceable structure under vibration. The electrode structure elements inserted into the spacers 86 and 88 may be wedged into the grooves 96, 106 and 116 to prevent looseness of the elements and hence reduce microphonics of the tube structure. The electrode elements and support structure are of rugged structure and allow assembly of the tube by automatic means. The assembly also provides complete shielding between two twin electrode structures within one envelope including the entire electrode structures and also extending below and above the electrode structure.

Referring in detail to Figs. 6 and 7, another modified design is shown in which complete shielding of a multiple type electron tube is obtained. This electrode assembly is also enclosed within a suitable envelope 10, such as described with respect to Figs. 1, 2 and 3, and is closed at the lower end with a button stem 12 through which are sealed the various prongs 18. These prongs 18 are connected on the interior of the envelope 10 to the various electrodes and act as lead-in members, as well as support for the electrode assembly 120. The prongs 18 may have welded to their inner ends short metal extensions 19 which may be easily bent to any desired position to ease the problem of connecting the various prongs 18 to the various electrodes.

The electrode assembly 120 shown in Figs. 6 and 7 is again a twin-type triode structure in which all of the elements of each triode structure 121 and 123 are separated and shielded from each other by means of a centrally located shielding member 122. The elements of the two triode structure's 121 and 123 are positioned by means of a lower insulating spacer 124 and an upper insulating spacer 126. The spacers 124 and 126 which may be of any suitable material, such as mica or ceramic, are positioned so as to be substantially perpendicular to the longitudinal axis of the envelope 10 and parallel to each other. In a well known manner, the spacers may be provided with openings to receive extension ears or tabs on the various electrode elements of the triode structures so as to position and retain the elements between the two spacer discs. The spacers could be in the form of the conventional circular disc-type configuration.

The lower and upper spacers 124 and 126 in the specific embodiment have two parallel edges and are provided with a centrally located slot 128 therein for positioning and fastening the shielding member 122. It may also be desirable to utilize only small tab openings on the spacers 124 and 126 and fasten the shield member 122 thereto in a well-known manner. The shielding member 122 shown in Figs. 6 and 7 has oppositely directed flange portions 130 extending at right angles from the main portion of the shielding member 122 in order to further enhance the shielding between the two electrode structures 121 and 123.

Referring in detail to the front portion of the electrode assembly 120, there is positioned one of the triode structures 121 which is of the similar construction and mounting as the rear triode structure 123. The triode structure 121 consists of a cathode 132, control grid 134, and plate or anode 136. The electrode elements 132, 134, and 136 are not threaded into apertures or slots in the spacers 124 and 126, as is the shielding member 122, but channels or notches are provided within the front edge of the spacers 124 and 126 so that the electrode elements 132, 134 and 136 may be inserted in a motion normal to the plane of the shielding member 122.

This type of assembly is permitted by providing two opposite edges on the spacers 124 and 126 which are generally parallel to the shielding member 122. The parallel edges of the spacers 124 and 126 are provided with notches 142, 144, 146 for receiving and fastening the electrode members without being positively fastened thereto. The lower and the upper spacers 124 and 126 are identical in structur and the mounting edge on which the front triode structure 121 is positioned is provided with an intermediate projecting portion 148 with the rectangular notch 142 therein having its long dimensions perpendicular to the plane of the shielding member 128. The cathode member 132 is mounted by means of this cathode notch 142 by pressing the cathode 132 into the slot 142 provided in both the upper and the lower spacers .124 and 126 in a motion normal to the plane of the center shield 128. The cathode 132 which may be of any suitable structure, such as an indirectly type heated cathode, comprised of a heater 131 positioned within a tubular metallic member 133 shown as having a rectangular cross section n this specific embodiment, and having suitable electron emissivematerial 135 on the two surfaces of the tubular member 133 having the greater dimensions. The length of the electron emissive coatings 135 on the tubular member 133 is slightly less than the distance between the upper and lower spacers 124 and 126, while the tubular member 135 extends both above and below the spacers 124 and 126. The cathode 132 may be secured within the cathode notch 142 by bending the upper and lower edges of portions of the large area cathode face outward as illustrated in Fig. 7.

I The grid electrode 134 is mounted in a similar manner as the cathode 132 in that it is inserted by a motion normal to the plane of the center shield 128 and seated so as to be fastened and positioned within notches 144 pro vided on the edge of the spacers 124 and 126 near the foot of the projection 148 provided for the cathode mounting. The control grid 134 is in the form of a generally U-shaped member with portions of the parallel legs serving as the active portions 150 of the grid 134. The grid 134 is comprised of a frame which is of a suitable material, such as nickel plated steel or molybdenum, with the active portions 150 comprised of parallel wires or a mesh positioned on the interior surface of the U-shaped member. The grid electrode 134 may be made in any well-known manner by automatic assembly and the fine lateral wires attached by suitable means, such as brazing, to the inner surface of the grid frame to extend over apertures provided therein for control of the electrons emitted from the cathode 132. The legs of the U-shaped grid frame are provided with oppositely directed extensions 152 which are, in turn, provided with spring means 154 on the end thereof, which are received by the grid notches 144 provided within the edges of the spacers 124 and 126, and are thereby fastened and retained without being positively fastened thereto. The spring means 154 is essentially a V-shaped portion which is inserted into the notch with the point of the V directed inwardly and so that the unattached leg of the V-shaped member will press outwardly against the interior edge of the notch 144. The notch 144 may be provided with a stepped edge so that the end of the unattached leg of the V-nember will press against said stepped portion. The length of the U- shaped grid frame and the oppositely directed extensions 152 is slightly less than the space between the upper and lower spacers 124 and 126, while the spring means portion 154 is of such a length as to extend below the bottom spacer 124 and above the top spacer 126 in order to fasten within the notches 144 provided in the spacer edges. A tab 156 may be provided on the upper and lower edge of the intermediate portion of the U-shaped grid 134 so t as to engage the cathode slot 142 provided in the projection portion 148 of the spacers 124 and 126.

The plate member 136 is also of a generally U-shaped configuration having the active portions 16!) thereof adjacent and parallel to the active portions 150 of the control grid 134. The active portions 161) in the plate memher 136 are also within the legs of the U-shaped member. Opposite directed extensions 16?. are provided on the legs of the U-shaped plate member 136 in a similar fashion to the grid member 134 with spring means 166 provided on the ends thereof for securing the plate member 136 within the plate notches 146 provided in the spacer edges 124 and 126 in a similar fashion as the grid member 134.

The tube structure shown in the drawings provide an extremeiy rugged type electrode structure and is superior over the conventional type electrode elements now utilized in the tube art which consist of two side rods with lateral wires supported thereon. It is necessary with prior design to thread the side rods within a lower mica spacer, and then attempt to thread the upper mica spacer over the upper ends of the electrode side rods. This operation is very difficult even if done by hand in that the electrode elements do not have a good base support, and as a result, donot stand upright and lean sideways. The elements are also weak and easily damaged in mounting. By use of the planar elements, the electrode elements are provided with a substantial base supportwhen mounted in the lower spacer so that the threading of the upper spacer over tabs or extensions provided in the electrode elements is easily done. The rugged structure would allow the use of the conventional type circular mica spacers with a structure such as described with respect to Figs. 6 and 7 without resorting to the mounting described in Figs. 6 and 7. However, the design shown in Figs. 6 and 7 lends itself even more so to mechanical assembly.

In the assembly of the device shown in Figs. 6 and 7, the top and bottom spacers 124 and 126 are fixed in position and held slightly away from the center shield 128 so as to ease the insertion of the electrode elements. The cathode 132 is first inserted in a motion normal to the plane of the center shield 128 and is secured in a manner previously described. The next step in the mounting would be the insertion of the grid 134 so that the spring means 154 would slide into the grid notches 144 and be fastened therein. The next operation would be the mounting of the plate member 136 also in a motion normal to the plane of the center shield 128, so as to be fastened within the plate notches 146 provided on the edges of the spacers 124 and 126. The assembly could be then rotated and the same insertion process be repeated for the electrode structure 123 mounted within the rear portion of the electrode assembly. The spacers 124 and 126 could then be pressed against the ends of the shielding member 128 and fastened thereto by means of the tabs provided on the shielding member 128.

It should be again emphasized that the structures described herein are directed primarily to simple twin triode structures, but it is obvious that the structures can easily be extended to other dual type tubes, such as twin pentodes or triode pentode structures, and still obtain the superior structural and shielding features described herein.

While we have shown our invention in several forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit and scope thereof.

We claim as our invention:

1. An electric discharge device comprising an envelope having an electrode assembly positioned therein, said electrode assembly comprised of two separate independent electrode structures, each of said electrode structures comprised of a plurality of planar type active portion electrode elements, said electrode elements consisting of at least a cathode, grid and anode and means positioning said elements within said assembly comprising a planar shielding member, and planar insulating spacers attached parallel to and contiguous with said shielding member, the cathodes of said electrode structures positioned and retained by means of compression between said two insulating spacers, said insulating spacers having channels provided in the exterior surface thereof for positioning the grids of each of said electrode structures accurately with respect to their respective cathodes.

2. An electric discharge device comprising an envelope having an electrode assembly positioned therein, said electrode assembly comprised of separate independent electrode structures, each of said electrode structures comprised of: a plurality of planar type active portion electrode elements consisting of at least a cathode, grid and anode, means positioning said elements within said assembly comprising a planar type shielding member centrally positioned within said envelope and parallel to the longitudinal axis of said envelope, two insulating spacers provided and fastened to said shielding member on each ide thereof having opposing tapered edges with notches provided therein, said notches positioned within said tapered edges so that a diametrically opposite notch is provided on each opposing edge mounting said electrode elements, said electrode elements having the planar active portions of the electrode elements parallel to said shielding member.

3. An electric discharge device comprising an envelope having an electrode assembly positioned therein, said electrode assembly comprised of separate independent electrode structures, each of said electrode structures comprised of a plurality of planar type active portion electrode elements consisting of at least a cathode, grid and anode, means positioning said elements within said assembly comprising a centrally located planar shielding member, sheet-like insulating spacers positioned parallel to each other and perpendicularly attached to said shielding member, notches provided in opposite edges of said insulating spacers positioning and fastening said electrode elements, said grid and said anode having a U-shaped central portion with the leg portions thereof constituting planar active portions, and spring means attached to oppositely directed extensions provided on the legs of said U-shaped central portions engaging said notches and retaining said grid and anode without being positively fastened to said insulating spacers.

4. An electric discharge device comprising an envelope having an electrode assembly positioned therein, said electrode assembly comprised of separate independent electrode structures, each of said electrode structures comprised of a plurality of planar type active portion electrode elements consisting of at least a cathode, grid and anode, means positioning said elements within said assembly comprising a centrally located planar shielding member, insulating spacers positioned parallel to each other and perpendicularly attached to said shielding member, notches provided on edges of said insulating spacer to position and fasten said electrode elements, said grid and anode being U-shaped with the leg portions thereof constituting planar active portions, and spring means provided to retain said leg portions within said notches without positively fastening said electrode elements to said insulating spacers.

5. An electron discharge device comprising a planar shielding element, a plurality of insulating spacer elements positioned substantially parallel to each other and attached perpendicular to said shielding element and having spaced notches on the periphery thereof, an electrode assembly comprising a plurality of U-shaped electrodes disposed adjacent opposite sides of said shielding element with each of said U-shaped electrodes including at least a pair of leg portions and at least one substantially planar active portion and with the ends of said leg portions having means to resiliently engage said notches to secure said electrodes in fixed position relative to said spacer elements so that said U-shaped electrodes may be assembled in said fixed position by movement of said electrodes in a perpendicular direction toward said shielding element.

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